At present, a helical scanning technique in which video tracks are obliquely traced on a tape by the rotary heads is the main type of scanning technique used in magnetic recording and reproducing systems (hereinafter, simply referred to as VTR). This type of scanning is employed in a VTR for use in the home to attain a miniaturized highly compact construction. For example, in VTR of the VHS system, the video signal is obliquely recorded on the tape having a width of 1/2 inch by use of two video heads arranged so as to be away from each other by 180.degree. on the rotary cylinder having a diameter of 62 mm. On one hand, in broadcasting VTR as well, a miniaturized and light-weight VTR is demanded for portable use for collection of news and for production of field programs, and VTR's of the U-standard of 3/4 inch are fairly used. For a news collection VTR, a high picture quality as well as small-size and light-weight is required for use in broadcasting. In the case of the U-standard VTR of 3/4 inch, there is a limitation of miniaturization since the cylinder diameter is 110 mm and the tape width is 3/4 inch. In addition, as for the recording method of the video signal, a method is adopted wherein the luminance signal is a frequency-modulated wave and the low frequency band is removed and the low frequency band converted carrier chrominance signal is added. Therefore, the frequency bands of the luminance signal and chrominance signal are limited and the picture quality is not necessarily satisfactory for use in broadcasting.
The small-sized and light-weighted system in which the reproduced image with a high picture quality is obtained has been proposed in consideration of the foregoing point (Japanese Patent Unexamined Publication No. 118490/1982). According to a system, the high quality image can be derived even by use of the cylinder of a diameter and the cassette of a size which are almost the same as those in the home-use VTR, and accordingly the system configuration can be miniaturized and made light-weight as compared with conventional news collecting VTR.
FIG. 1 is a plan view of an arrangement of the heads on the cylinder for use in the foregoing system. FIG. 2 is a front view of the heads appearing in FIG. 1. FIG. 3 is a diagram showing an example of the recorded patterns by the heads. FIG. 4 is a block diagram of one embodiment of the recording system using the heads. FIG. 5 shows a waveform diagram of the main part in FIG. 4. The recording system will then be described with reference to FIG. 4.
In FIGS. 1 and 2, reference characters A.sub.1 (A.sub.2), A.sub.1 ' (A.sub.2 ') and B.sub.1 (B.sub.2), B.sub.1 '(B.sub.2 ') denote two pairs of heads arranged at the positions on the circumference of the cylinder, which are away from each other by an angle of 180.degree., such that they are aligned at the same height of the cylinder. In FIG. 3, A, A', B, and B' indicate loci written by the heads A.sub.1, A.sub.1 ', B.sub.1, and B.sub.1 ', respectively. In FIGS. 2 and 3, T.sub.A and T.sub.B denote track widths of the heads A.sub.1 (A.sub.1 ') and B.sub.1 (B.sub.1 '), respectively, T.sub.P indicates a track pitch, and T.sub.S represents a space. When the diameter and rotating speed of the cylinder, the values of x and y in FIG. 2, the values of T.sub.A, T.sub.B and T.sub.S, the tape speed, and the angle between the tape and the record locus are now properly determined, the loci as shown in FIG. 3 are obtained when the heads are arranged at the positions as shown in FIGS. 1 and 2. For example, it is possible to constitute the VTR having the cylinder of substantially the same diameter as that in the VHS system VTR and being capable of recording for about twenty minutes by use of the VHS cassette tape. If a metal tape or the like is used, recording for 60 to 90 minutes can be performed.
As a method of recording and reproducing the color video signal by the recording and reproducing system as mentioned above, there is a method whereby the (frequency modulated) luminance signal is recorded by the A.sub.1 (A.sub.1 ') head and the (frequency modulated) chrominance signals are recorded by the B.sub.1 (B.sub.1 ') head. With such a method, the track width of the luminance signal can be enlarged and at the same time the frequency band can be set to be wide since no chrominance signal is added, so that a reproduced image of having a high S/N ratio and a high resolution can be obtained. In addition, with respect to the chrominance signals as well, the base band signals (for instance, the R-Y and B-Y signals) can be recorded as frequency modulated signals; therefore, a reproduced signal of a high frequency band and a high S/N ratio can be obtained. It is possible to construct the small-sized and light-weight VTR with a high quality having a cylinder and a cassette of substantially the same size as those in the home use VTR and being capable of recording for 60 to 90 minutes.
In FIG. 1, heads A.sub.2 (A.sub.2 ') and B.sub.2 (B.sub.2 ') arranged at the positions which are delayed by 60.degree. from the heads A.sub.1 (A.sub.1 ') and B.sub.1 (B.sub.1 ') are used for reproduction. The recording is performed using the A.sub.1 (A.sub.1 ') and B.sub.1 (B.sub.1 ') heads and at the same time the reproduction is performed (simultaneous reproduction) to thereby check the recorded state. Or, those reproducing heads are arranged on movable elements such as piezo-electric elements or the like so that the record tracks are accurately traced in a special reproducing mode, thereby enabling the reproduction of a noise-free video image.
The recording system of FIG. 4 will be described hereinbelow with reference to FIGS. 3 to 5. In FIG. 4, reference numeral 1 denotes a Y signal (luminance signal) input terminal; 2 is an R-Y signal input terminal; 3 a B-Y signal input terminal; 4 a time-axis compressor; 5 and 6 frequency modulators; 7 and 8 recording amplifiers; 9 (9') and 10 (10') video heads; 11 and 12 reproducing amplifiers; 13 and 14 frequency demodulators; 15 a time-axis expander; 16 a Y signal output terminal; 17 an R-Y signal output terminal; and 18 a B-Y signal output terminal.
In FIG. 5, reference numerals 1, 2 and 3 denote waveforms of the input Y signal, R-Y signal and B-Y signal, respectively, (horizontal sync signals are added also to the R-Y and B-Y signals for the purpose of convenience). Numeral 19 denotes a waveform of an output signal of the time-axis compressor 4 and is a waveform at the position indicated by the numeral in FIG. 4. The Y signal applied to the Y signal input terminal 1 is modulated by the frequency modulator 5 and is amplified by the recording amplifier 7, and thereafter it is recorded on the tape by the head 9. The Y signal has a frequency band of about 4.5 MHz and the frequency deviation for modulation is set to, for instance, 5 to 7 MHz to record and reproduce the Y signal with good performance. The R-Y signal and B-Y signal applied to the R-Y signal input terminal 2 and B-Y signal input terminal 3 are time-axis compressed and synthesized by the time-axis compressor 4 in such a manner that the R-Y signal appears in the former half portion and the B-Y signal appears in the latter half portion of one line (1H), as shown in the waveform 19 in FIG. 5. This synthesized signal is modulated by the frequency modulator 6 and is amplified by the recording amplifier 8, and thereafter it is recorded on the tape by the head 10. Since the R-Y and B-Y signals have a frequency band of about 1.5 MHz, the synthesized signal derived by compressing the time axis of each signal to 1/2 has a frequency band of about 3 MHz. The frequency deviation of this synthesized signal is set to, e.g., 4 to 6 MHz. FIG. 3 shows the tape pattern obtained by recording the Y signal and chrominance signal by way of the two pairs of heads having the above-mentioned structure in this manner. In FIG. 3, A and A' denote the record loci of the Y signal, while B and B' indicate the record loci of the chrominance signal. As shown in FIG. 3, with respect to the Y signal in case of the 20-minute recording, the track width is set to be wider than that in a conventional home use VTR. On the other hand, for the chrominance signal, the FM carrier frequency is low and the frequency band is about 3 MHz, so that the reproduction can be performed with a good S/N ratio. Moreover, the use of the metal tape or the like makes it possible to perform the recording for 60 to 90 minutes without deterioration of performance. Upon reproduction, the Y signal reproduced by the head 9' is amplified by the reproducing amplifier 11 and is demodulated by the frequency demodulator 13, so that the reproduced Y signal is derived from the output terminal 16. On the other hand, the chrominance signal reproduced by the head 10' is amplified by the reproducing amplifier 12 and is demodulated by the frequency demodulator 14, and thereafter it is expanded by the time-axis expander 15 and is separated into the original R-Y signal and B-Y signal. Thus, the reproduced R-Y signal and B-Y signal are obtained from the output terminals 17 and 18. This reproduction can be performed simultaneously with the recording (simultaneous reproduction).
As described above, according to the system of FIG. 4, a reproduced image of a high quality can be obtained and the simultaneous reproduction and a noiseless search can be also carried out. However, with regard to the audio signals, only the conventional linear track is provided, so that the S/N ratio is about 50 to 55 dB and there is a limitation of performance.
A PCM recording system whereby the audio signals are digitized and recorded has been recently put into practical use as a recording/reproducing method for obtaining audio signals of a high quality. As a method for audio PCM recording in a VTR, in case of the two-head helical scan VTR, there is a method whereby the wrap angle of tape onto the rotary cylinder is set to a value larger than 180.degree. and the time-axis compressed PCM audio signals are recorded into the overlap portion. FIG. 6 shows the timing relationship between the video and audio signals according to this method and FIG. 7 shows a recorded pattern. In FIGS. 6 and 7, reference numeral 20 denotes an input video signal; 21 an input audio signal; 22 a recorded audio PCM signal which was time-axis compressed; and 23 a reproduced audio signal which was returned to the original states. Reference characters v.sub.1, v.sub.2, . . . denote signals for every field of the video signal; a.sub.1, a.sub.2, . . . are audio signals corresponding to v.sub.1, v.sub.2, . . . ; a.sub.1, a.sub.2, . . . are compressed PCM signals of a.sub.1, a.sub.2, . . . ; and a.sub.1, a.sub.2, . . . are reproduced audio signals which were returned to the original states. As shown in FIGS. 6 and 7, the audio signals are processed on a one-field unit basis; therefore, they are delayed by one frame from the corresponding video signals through the recording and reproduction. If the dubbing or the like is repeated in this state, this delay difference is increased one by one, causing a serious inconvenience. To prevent this, it is sufficient to provide other separate heads adapted to reproduce only the audio signals in a manner such that it is preceded by over one frame. However, in case of the arrangement as shown in FIG. 2, the number of heads including the rotary heads for erasure and the, like becomes extremely large; therefore, this construction is practically difficult.